This invention relates to air-vapor mixers for internal combustion engines and is particularly directed to an improvement in the fuel valve of the air-vapor mixer wherein a combination action of the material composing the fuel valve and the configuration of the fuel valve itself improves engine performance.
Internal combustion engines fueled by propane, butane, a mixture of propane and butane, or natural gas utilize an air-vapor mixer in their fuel supply system to mix the fuel with air for combustion in the engine. It is advantageous for an internal combustion engine to operate on as lean a mixture as is possible without misfiring, especially at low and intermediate loads, because to do so results in higher fuel efficiency and a minimum output of pollutants such as hydrocarbons and carbon monoxide (CO). However, lean mixtures will not generally burn reliably under some engine conditions such as starting, idling and deceleration. Accordingly, it is desirable to enrich the charge under conditions where misfiring may occur but to lean the charge under other conditions, such as low and intermediate load level operating conditions, so that a nearly stoichiometric relationship of carbon and oxygen is achieved.
In response to this need, the fuel valve of the present invention is composed of an acetal copolymer resin marketed under the trademark Duracon by the Eiko Company in Japan. The simple linear chain structure(--OCH.sub.2 --).sub.n and the relative shortness of the carbon-oxygen bond impart properties of high crystallinity and relatively high density to acetal resins in the solid state. This material has the qualities of high stiffness, excellent dimensional stability, high tensile and impact strength, good abrasion resistance, and a low coefficient of friction. This combination of mechanical properties makes the Duracon acetal copolymer suitable as a replacement for metals in a variety of applications.
Besides dimensional stability, an important characteristic of Duracon in the fuel valve of the present invention is its high coefficient of linear thermal expansion over that of metals used in the body of the mixer, e.g. aluminum. The fuel valve, therefore, when cool and in its contracted state creates a larger effective size of the metering orifice in which it operates. When richer mixtures are required for cold starting and idling, the fuel valve, being in this contracted state, provides the larger effective orifice and, therefore, the richer mixture. As the internal combustion engine is heated from this cool state the fuel valve increases in size and, due to its high coefficient of expansion relative to the surrounding metal, thereby leans the mixture for operating conditions such as low and intermediate load levels.
The fuel valve is also provided with an incrementally decreasing perimeter that causes the diameter of the valve to vary in a step-by-step fashion along its operating length or axis. This stepped configuration provides close control of the carbon/oxygen relationship over the mid-range of engine operating speeds. Prior art valve cones with uniform conical surfaces unnecessarily enrichened the mixture with the result that the engine developed high power but at the cost of fuel economy.
It is, therefore, an important object of the present invention to provide an improved fuel valve for an air-vapor mixer which expands to lean the mixture when the engine warms up and effectively controls the mixture over the mid-range of operating speeds to achieve an optimal, nearly stoichiometric relationship of carbon and oxygen.
Another important object of this invention is to provide an improved fuel valve for an air-vapor mixer which has a significantly higher coefficient of thermal expansion than the material defining the metering orifice in which the valve operates, thereby decreasing the effective orifice size to lean the mixture as the internal combustion engine increases in temperature after starting.
Still another important object of this invention is to provide an improved fuel valve for an air-vapor mixer which enables a predetermined, optimal admixture of carbon and oxygen to be maintained over the mid-range of engine speeds, thereby increasing efficiency and minimizing exhaust pollutants.
Furthermore, it is an improtant object of this invention to provide a temperature compensating fuel valve as aforesaid which improves fuel economy and reduces exhaust pollutants while retaining high operational performance including richer mixtures for cold starting and idling.
Additionally, an important object of this invention is to provide a fuel valve as aforesaid with optimal mid-range control in which such control is achieved by a stepped valve surface, each step optimizing the carbon/oxygen admixture for a corresponding engine speed within the mid-range of operation.